Reconfigurable logic fabrics for integrated circuits and systems and methods for configuring reconfigurable logic fabrics

ABSTRACT

In accordance with the present invention there are provided herein asynchronous reconfigurable logic fabrics for integrated circuits and methods for designing asynchronous circuits to be implemented in the asynchronous reconfigurable logic fabrics.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.12/304,694, filed May 26, 2009, now issued as U.S. Pat. No. 7,880,499,which is a U.S. National Stage Filing under 35 U.S.C. 371 fromInternational Application No. PCT/US2007/072300, filed Jun. 27, 2007 andpublished in English as WO 2008/008629 A2 on Jan. 17, 2008, which claimsthe benefit of priority under 35 U.S.C. 119(e) to provisionalapplication Ser. No. 60/817,552 filed on Jun. 28, 2006, whichapplications and publication are incorporated herein by reference intheir entireties.

FIELD OF THE INVENTION

The present invention relates to integrated circuits comprisingreconfigurable logic fabrics and more specifically to a high performancereconfigurable logic fabric for deployment in integrated circuitsincluding for example, field programmable gate arrays (FPGAs),application specific integrated circuits (ASICs) and other programmablelogic devices where computational speed is a consideration in circuitdesign. The invention also relates to methods and apparatus forconfiguring high performance reconfigurable logic fabrics.

BACKGROUND OF THE INVENTION

Conventional reconfigurable logic fabrics rely on sequentialarrangements of synchronous circuits embedded within the fabric. Thepresence of synchronous circuits arranged in sequence within the fabriclimits the speed at which a logic fabric can perform logical operations.Each circuit in the sequence chain must wait at least one clock cycle toreceive the results of the computation of the previous circuit in thechain. This delay limits the speed at which conventional reconfigurablelogic fabrics can operate. The present inventors have recognized theneed for reconfigurable logic fabrics capable of operating at fasterspeeds than can be obtained using conventional synchronous logicfabrics.

Configuring conventional reconfigurable logic fabrics to comprisespecific hardware circuit implementations is accomplished using off-lineelectronic design automation (EDA) tools. These tools presume thepresence of synchronous circuits in the reconfigurable fabric. Thepresent inventors have recognized the need for a reconfigurable logicfabric that is not only capable of faster computational speeds, but isalso amenable to design using available EDA design tools.

SUMMARY OF THE INVENTION

The invention provides reconfigurable logic fabrics and methods andsystems for configuring reconfigurable logic fabrics.

DESCRIPTION OF THE DRAWING FIGURES

These and other objects, features and advantages of the invention willbe apparent from a consideration of the following detailed descriptionof the invention considered in conjunction with the drawing figures, inwhich:

FIG. 1 is a conceptual diagram illustrating dataflow nodes suitable forrepresenting asynchronous circuits operations to be implemented in aprogrammable logic fabric according to embodiments of the invention.

FIG. 2 illustrates a floor plan for a portion of a programmable logicfabric according to an embodiment of the invention.

FIG. 3 is a block diagram of a logic cluster according to an embodimentof the invention.

FIG. 4 is a circuit diagram of a logic cluster pair according to anembodiment of the invention.

FIG. 5 is a circuit diagram illustrating logic clusters including anarrangement of reconfigurable logic blocks implementing a wide ANDoperation according to an embodiment of the invention.

FIG. 6 is a circuit diagram illustrating an arrangement ofreconfigurable logic blocks implementing wide OR operations according toan embodiment of the invention.

FIG. 7 is a circuit diagram illustrating a reconfigurable logic blockaccording to an embodiment of the invention.

FIG. 8 is a circuit diagram illustrating a lookup tables configured in aloop in accordance with an embodiment of the invention.

FIG. 9A is a logic diagram illustrating a logic element of the inventionconfigured to carry out a merge operation.

FIG. 9B is a logic diagram representing a logic element capable ofreconfiguration to carry out logic operations illustrated in FIGS. 9Aand 9C.

FIG. 9C is a logic diagram illustrating a logic element of the inventionconfigured to carry out a split operation.

DETAILED DESCRIPTION OF THE INVENTION

In accordance with the present invention there are provided hereinasynchronous reconfigurable logic fabrics for integrated circuits andmethods for designing asynchronous circuits to be implemented in theasynchronous reconfigurable logic fabrics.

FIG. 1

FIG. 1 illustrates example asynchronous dataflow operations 102-114. Inone embodiment of the invention dataflow operations 102-114 definespecific hardware implementations for an asynchronous reconfigurablelogic fabric. Data for dataflow operations are represented as “tokens”.Data tokens follow data paths. In FIG. 1 data paths are represented asedges.

For example, a copy operation 102 describes an operation whereby a nodeof a circuit duplicates a token at its token input and sends it to aplurality of receivers. A function 104 computes an arbitrary function ofa plurality of input variables and provides the result at an output.According to embodiments of the invention a function does not completeuntil tokens arrive on all of its inputs.

A merge operation 106 is represented as a node comprising a plurality ofinputs, a control input (ctrl), and a single output. The merge operation106 reads a control token from the control input. The control tokenindicates the input from which the merge will read a token to provide onthe output channel. A split 108 performs the opposite function of amerge. Split 108 has one input and a plurality of outputs. The value ofthe control token indicates the output to which the split will write thetoken read from the input channel.

A sink 110 consumes tokens unconditionally. A source 112 generates datatokens with a constant value. A source 112 does not produce a new tokenuntil its previous token is consumed. An initializer 114 begins with adata token on its input when a device, for example an FPGA, resets.After reset, initialize 114 behaves as a copy.

The operations described above as illustrated in FIG. 1 are used todescribe hardware circuit implementations for specific configurations ofa reconfigurable logic fabric according to an embodiment of theinvention. Design tools implementing the basic operations illustrated inFIG. 1 can be used to configure the asynchronous reprogrammable logicfabric of the invention. The basic operations are combinable toimplement circuits capable of performing more complex deterministicasynchronous computations using reconfigurable logic fabric of theinvention.

The reconfigurable asynchronous logic fabric of the invention providesat least two benefits. First, the circuits comprising the fabric arecapable of faster operation due to clock independent operation. Second,a representation of asynchronous circuits that will comprise fabrics ofthe invention is readily implemented using available design tools. Thusthe embodiments of the invention optimize performance of circuitscarrying out the dataflow operations described above.

FIG. 2

FIG. 2 illustrates an integrated circuit 200 according to an embodimentof the invention. Integrated circuit 200 comprises programmable logicfabric 201 and programmable input output (I/O) blocks 202. Logic fabric201 comprises at least one fabric portion 250. A fabric portion 250comprises an array 210 of elements embedded within logic fabric 201.Elements of portion 250 comprise at least one of each of the flowingunits (also referred to herein as blocks): Reconfigurable Logic Block(RLB) 208, Static Memory Block (SMB) 206 and Asynchronous MultiplierBlock (AMB) 207.

In one embodiment of the invention each of the elements comprising logicfabric 201 of the invention is asynchronous, that is, capable ofperforming logic operations independent of a clock signal. Consequently,logic fabric 201 is capable of carrying out logical operations at higherspeeds than can be achieved by conventional fabrics which rely onsynchronous logic elements.

In one embodiment of the invention logic fabric 201 of the inventioncarries out logical operations at speeds comparable to clock speeds ofat least 1 GHz. According to one embodiment of the invention acommercially available complementary metal-oxide semiconductor (CMOS)process is employed to embed elements within logic fabric 201.Programmable logic fabric 201, configured in accordance with embodimentsof the invention described herein provides reprogrammable logic circuitsfor deployment in electronics equipment operating in high speedenvironments.

In one embodiment of the invention programmable logic fabric 201provides a scalable fabric floor plan, i.e., architecture, comprising atleast one array 210 of logic fabric elements. The programmable fabric201 of the invention is deployable in a wide variety of semiconductordevices including, but not limited to, systems-on-chip (SoCs),application specific integrated circuits (ASICs), field programmablegate arrays (FPGAs), systems-in-a-package (SiPs), and applicationspecific standard purpose (ASSP) devices.

Embodiments of fabric 201 are implementable by commercially availableasynchronous logic families. Other embodiments of the invention areimplemented using a combination of logic families. Examples of suitablelogic families include quasi delay-insensitive circuits, self-timedcircuits, speed independent circuits, bundled data circuits,micropipelines, asP, asP*, and GasP, as well as single track full buffercircuits, self-resetting/pulse-mode logic, or other circuits that useasynchronous techniques.

SRAM Memory Blocks (SMBs)

SMBs 206 are memory elements. According to one embodiment of theinvention SMBs 206 comprise dual-port Static Random Access Memory (SRAM)modules. At least one SMB 206 is embedded in an array 210 ofprogrammable logic fabric 201. An SMB 206 is accessible by RLBs 208 andAMBs 207. An SMB 206 is configurable to comprise at least one of aplurality of memory arrangements. Example memory arrangements for SMBs206 include: 32K×1-bit; 16K×2-bit; 8K×4-bit; 4K×8-bit; 4K×9-bit;2K×16-bit; 2K×18-bit; 1K×32-bit; 1K×36-bit; 512×64-bit; 512×72-bit.

The 9-, 18-, 36-, and 72-bit memory configurations of SMB 206 provide anextra bit for every byte of memory. According to some embodiments of theinvention the extra bit is usable for parity checking. An SMB 206 iscoupled to an interconnecting grid (not illustrated in FIG. 2) via aprogrammable interconnect element CB 204. An SMB 206 is also coupled toits neighboring elements, e.g., an AMB 207. According to one embodimentof the invention CB 204 provides an asynchronous interface for SMBs 206to the interconnecting grid. In one embodiment of the invention CB 204is asynchronous and pipelined. In asynchronous operation memoryread/write requests are transmittable to SMB 206 before the previousread/write request has been satisfied by an SMB 206. In one embodimentof the invention SMB 206 is configurable to comprise an asynchronousFirst In First Out (FIFO) memory. In such an embodiment SMB 206 isconfigured as a circular buffer and includes logic to support insert andremove operations. In one embodiment of the invention the number ofFIFOs embedded within logic fabric 201 and the number of ports to an SMB206 is reprogrammable.

Asynchronous Multiplier Blocks (AMBs)

An AMB 207 comprises an asynchronous reconfigurable multiplier. AMB 207is coupled to at least one SMB 206. Each SMB 206 has a neighboring AMB207. A neighboring AMB 207 is configurable to perform signedmultiplication at various widths. AMB 207 is programmable for a varietyof multiplier configurations including, but not limited to: a single72×72-bit multiplier; four 36×36-bit multipliers; eight 18×18-bitmultipliers; sixteen 9×9-bit multipliers.

AMB 207 as described herein provides higher density and lower powerconsumption for integrated circuit 200 compared to multipliersconstructed from RLBs. AMB 207 is configurable to write to and read fromthe interconnecting grid (not shown) by programming its associatedinterconnect element CB 204. An AMB 207 is also configured forcommunication directly with its adjacent SMB 206. This configuration ofAMB and CB enables efficient programmable configuration of circuits, forexample, multiply-accumulate circuits. In one embodiment of theinvention multiply accumulate circuits are formed by configuring an RLB208 as an accumulator and by configuring AMB 207 as a multiplier andemploying an SMB 206 for storage. This arrangement of SMB, AMB and RLBis usable to implement a wide variety of digital signal processing (DSP)functions such as fast Fourier transform (FFT), finite impulse response(FIR) filters, and discrete cosine transform (DCT). Accordingly RLB ofthe invention are configurable to implement multipliers for applicationsdemanding multiplication resources that would be inefficient to provideby an AMB 207 alone.

Channel Boxes (CB) 220 and Switch Boxes (SB 205)

Logic fabric 201 comprises a plurality of channel boxes (CB) 220 and aplurality of switch boxes (SB) 205. Each RLB 208, SMB 206 and AMB 207 iscoupled to a corresponding portion of an interconnecting grid of fabric201 via a corresponding channel box CB 220. Switch boxes (SB) 205 areprovided at intersecting portions of the pipelined interconnecting grid.SB 205 is programmable to couple elements of fabric 201 acrossinterconnecting grid portions. Configuration of array 210 isaccomplished by coupling fabric elements to the interconnecting grid byprogramming of channel boxes 206 and switch boxes 205 to executedataflow operations such as those described with respect to FIG. 1 suchthat reprogrammable logic fabric 201 comprises an asynchronousreconfigurable logic fabric.

Reconfigurable Logic Blocks (RLB) 208

In one embodiment of the invention reprogrammable logic blocks (RLBs)208 comprise logic circuits. Logic circuits carry out logical operationson signals provided at logic circuit inputs to provide an operationresult at a logic circuit output.

In one embodiment of the invention each RLB of logic fabric 201comprises only asynchronous logic circuits. Thus, the invention is adeparture from conventional logic circuits and fabrics. Conventionalprogrammable logic fabrics comprise synchronous circuits through thefabric. Thus, conventional fabrics require a clock to synchronizecomputation operations. In contrast, fabric 201 of the invention doesnot rely on a clock to synchronize computation operations. Because RLBs208 comprise asynchronous logic circuits, fabric 201 does not require aclock distribution network.

In one embodiment of the invention an RLB 208 comprises an arrangementof logic clusters LCs 400.

Logic Cluster 400

FIG. 4 illustrates a logic cluster (LC) 400 according to an embodimentof the invention. In one embodiment of the invention each RLB comprisesa group of four LC 400. (Example illustrated in FIG. 5.) Each LC 400 isprogrammable to operate in sequence such that RLB 208 is configurable tocarry out complex logic operations on signals provided across aplurality of LC inputs. LC 400 inputs are indicated at A, B, C and D inFIG. 4.

FIG. 4 is schematic of a Logic Cluster 400. Unlike traditionalreconfigurable logic circuits, LC unit 400 comprises asynchronous logiccircuits. In one embodiment of the invention the asynchronous logiccircuits are pipelined. LC unit 400 comprises a four-input lookup table(LUT) 402, a programmable AND (PAND) 406 an XOR gate (PXOR) 408, and acarry-chain mux (CMUX) 410 and a programmable multiplexer (PMUX) 412.LUT 402 implements functions comprising up to four inputs. To implementfunctions with less than four inputs, the sources in the RLB are used togenerate tokens for the unused inputs. The output of the LUT 402 iscoupled through a programmable XOR buffer (PXOR) 408 to the output of LC400 or to its corresponding state bit 413. An embodiment of theinvention PXOR 408 is programmable to act as a buffer. AlternativelyPXOR 408 is programmable to perform an XOR operation between the outputof the LUT 402 and a carry-in value provided at Cin 401.

Each LC unit 400 comprises circuitry for dedicated early-out carrychains, which can be used with the PXOR 408 to efficiently implementripple-carry adders. The carry mux (CMUX) 410 is programmable to use theoutput of LUT 402 resulting from an operation implemented by LUT 402 anda carry-in token 401 to determine the correct carry-out token 403. Ifthe carry-in token 401 is not required for determining the carry-outtoken 403 (for example, if the values of both inputs to a one-bit adderare zero, the carry out will be zero). In that case CMUX 410 generates acarry-out token at 403 before the carry-in token arrives at 401. Each LCunit 400 can therefore be configured as two bits of a full adder, withthe carry chain going from bottom to top. The carry-chain circuitry alsocontains the programmable AND unit (PAND), which can be used forimplementing multipliers.

Logic Cluster Pair 300

FIG. 3 illustrates a logic cluster pair 300. Logic cluster pair 300comprises two 4-input Look Up Tables (LUT) 302, 304, arithmetic andcarry logic 306, 308, and state bit storage elements 310, 312. Theoutput of each LUT 302,304 is configurable to drive the correspondingoutput of a LC and a corresponding state bit. In one embodiment of theinvention the output of a LUT 302 is selectable to drive thecorresponding output of the LC or the state bit. A PLI (best illustratedin FIG. 7) is configurable such that the output of a state bit(indicated at 310 and 312) is an input to an LUT 302, 304). Thisconfiguration enables state-holding computations.

According to one embodiment of the invention arithmetic and carry logic306 and 308 are configured to provide early-out carry chains. In thisconfiguration an RLB is capable of generating a result of a logicoperation as soon as the output can be determined. The RLB generates theresult without waiting for all the inputs to be ready. By concatenatingarithmetic and carry logic blocks 306 and 308 in the manner shown inFIG. 3, the average latency of the block is reduced. In one embodimentof the invention the blocks including the LUT, arithmetic and carrylogic, and state bit are all pipelined and implemented with asynchronouslogic.

In addition to logic clusters, RLBs 208 according to embodiments of theinvention further comprise token sources and sinks, two way conditionalunits, four way conditional units, and eight way conditional units. RLBsconfigured in accordance with embodiments of the invention allowefficient mapping of logic operations to architecture of fabric 201.Each RLB sends and receives data tokens to and from the pipelinedinterconnect by using its adjacent CBs, as shown in FIG. 2.

Programmable I/O Blocks 202

Programmable I/O blocks 202 (illustrated in FIG. 2) are configurable toenable logic fabric 201, and thus integrated circuit 200 to be coupledfor operation in synchronous circuits, devices and systems. In oneembodiment of the invention programmable I/O blocks 202 are arrangedaround the perimeter of logic fabric 201, for example to form aperimeter portion of integrated circuit 200. In one embodiment of theinvention I/O blocks comprise programmable synchronous I/O blocks andstatic synchronous and asynchronous I/O blocks.

One example embodiment of the invention comprises an FPGA implementedusing two types of I/Os. In one embodiment of the invention the typesare selectable. The first type comprises synchronous I/O banks (SIOs),which comprise a combination of standard synchronous I/O blocks as wellas configurable synchronous blocks [e.g. FIG. 2 at 288] that can convertfrom the asynchronous fabric to a synchronous interface. Converter unit288 includes an input coupled to outputs of the asynchronous elements oflogic fabric 201 to receive logic operation results. The converter unit288 provides the operation results synchronously at a converter output.The second type comprises asynchronous I/O banks (AIOs), which can beused for asynchronous and high-speed communication between a pluralityof FPGAs.

According to some embodiments of the invention programmable I/O blocksare configured in accordance with a technical standard that specifieselectrical input output unit characteristics. Examples electricalstandards with which embodiments of I/O blocks of the invention conforminclude, but are not limited to GPIO, PCI, PCI-X, LVDS, LDT, SSTL, andHSTL. Accordingly signals coupled through I/O blocks will comprise avariety of voltages and drive strengths depending on the specificapplication in which the invention described herein is implemented.

Synchronous I/O (SIO) Banks

According to embodiments of the invention integrated circuit 200includes I/O banks 202. I/O banks 202 enable asynchronous fabric 210 tointerface with synchronous logic circuits. In one embodiment of theinvention I/O banks 202 are arranged about the perimeter of programmablelogic fabric 201. I/O banks 202 provide high-throughput communicationbetween two asynchronous ICs 200, for example two FPGAs. According toembodiments of the invention such communication is accomplished withoutthe drawback of synchronous conversion. I/O banks 202 are configurablefor two types of asynchronous communication. The first type is astandard asynchronous handshake protocol using a bundled-data interface.The second type is a high-speed serial link enabling, for example,FPGA-to-FPGA communication.

The bundled-data interface uses a set of I/O pins for data, plus a pairof request/acknowledge pins to implement a standard bundled dataasynchronous handshake protocol. I/O banks 203 are configurable toimplement at least one of a four-phase handshake and atransition-signaling two-phase protocol. I/O band 203 is configurable toimplement sender initiated and receiver initiated protocols. Theprotocol is implementable using a selectable number of I/O pins up to alimit comprising the number of portions of I/O block 202 comprisingasynchronous I/O banks. The physical signaling for the protocol isselectable by a programmable signaling block.

A serial link protocol that allows multi-Gbps throughput for high-speedFPGA-to-FPGA communication is also implementable using I/O blocks 202.This serial link provides high-bandwidth and low latency asynchronouscommunication without any re-synchronization overhead.

In one embodiment of the invention asynchronous to synchronousconversion is effected by Electronic Design Automation (EDA) tools. EDAtools are usable to define an I/O as providing a synchronous outputduring design of IC 200. EDA tools provide converters comprisingprogrammable clock generators.

According to embodiments of the invention EDA converters are used tospecify the frequency of the programmable I/O blocks 202. Fabric 201 ofthe invention permits use of EDA converters. Reconfigurable fabric 201is configurable for operation at frequencies specified by the clockgenerator of the EDA tool. Thus the invention enables use of EDA toolsand consequently, the use of synchronous-to-asynchronous convertersprovided by EDA tools. The use of EDA converters also provides adelay-locked loop to enable a synchronous output of IC 200 to be validat a fixed delay offset from a clock edge.

EDA tools provide a second class of converters that enable synchronousoutput with a valid bit for IC 200. In that case an operation result isproduced whenever fabric 201 generates a new data output. The physicalsignaling for a protocol is selectable from a programmable signalingblock according to some embodiments of the invention.

The asynchronous architecture of fabric 201 supports synchronoustroubleshooting integrated circuit 200. In one embodiment of theinvention IC 200 comprises asynchronous to synchronous converters 288that can be activated in a user-specified manner. Key registers or wiresare specified as “debug” signals. These will automatically be connectedto on-chip debug registers of IC 200. A debug register can be scannedand loaded, with the clock used to step through the execution in asequential manner similar to a synchronous flow. An entire set of debugregisters and I/Os can be scanned or loaded via the Joint Test ActionGroup (JTAG) interface. As is known in the art, JTAG refers to the IEEE1149.1 standard, Standard Test Access Port and Boundary-ScanArchitecture for test access ports used for testing printed circuitboards using boundary scan.

FIG. 5 Reconfigurable Logic Blocks (AND Configuration)

FIG. 5 is a circuit diagram illustrating logic clusters such as thoseillustrated in FIGS. 3 and 4 arranged to comprise reconfigurable logicblocks (RLBs) 501,503 and 505 according to a simplified example of anembodiment of the invention. In the embodiment illustrated in FIG. 5RLBs 501,503 and 505 are configured to implement a wide AND operation.Each RLB comprises circuit elements providing wide AND, OR, andsum-of-products (SOP) operations. Wide AND operations that span multipleRLBs are formed by programming LUTs (e.g., 502, 504) to perform 4-inputAND operations and by using the carry chains. FIG. 5 shows a 48-inputAND that spans RLBs 501,503 and 505. In one embodiment of the inventionthe AND is pipelined. In other words the bottom-most LUT 530 accepts newinputs as soon as LUT 530 produces its output. LUT 530 need not wait forthe entire 48-input AND to complete.

With reference particularly to FIG. 5, each of six logic clusters (LC)514, 516, 518, 520 and 522 includes two four-input LUTs (e.g., LUT 502and 504 of LC 518) performing an AND function on the inputs and feedingthe output to a chain of CMUXs (e.g. CMUS 508 and 506 of LC 518). The 64input lines are formed in groups of sixteen each (e.g., inputs to LUT502,504,533 and 530 of LCs 518 and 520 of RLB 503). As described above,each of the LCs comprises two LUTs and the connecting arithmetic logic(AL) as described above.

FIG. 6 Reconfigurable Logic Blocks (OR Configuration)

FIG. 6 is a circuit diagram illustrating an arrangement ofreconfigurable logic blocks implementing wide OR operations according toan embodiment of the invention. In contrast to the wide AND operations,which flow vertically using the dedicated carry connections betweenadjacent RLBs, wide OR operations flow horizontally through dedicatedhorizontal connections. Each RLB contains a programmable OR buffer (POR)that can have up to nine inputs: the outputs of each of the LCs, and theoutput of the POR from the left-adjacent RLB via a dedicated horizontalconnection. This enables a single RLB to perform a 32-input OR. FIG. 6shows four RLBs 602A, 602B, 602C, 602D arranged to form a 128-input OR600. One exemplary RLB 602B is expanded to show the inclusion of eightfour-input LUTs each programmed to perform an OR function with theoutputs combined into an eight-input plus carry POR.

By combining the techniques used to create wide AND and OR operations, auser can efficiently implement very wide sum-of-product (SOP)operations. The programmable OR circuit is pipelined, and the POR cangenerate its output before all its inputs are ready. For example, if oneof the input tokens is “1” then the output of the POR is known eventhough all the other inputs are not ready as yet. The POR produces anearly-out “I” value that allows the rest of the circuit to proceed eventhough all the inputs may not be ready. Alternative designs can vary thenumber of inputs supported by the POR.

FIG. 7

FIG. 7 is a circuit diagram illustrating a reconfigurable logic block(RLB) 700 according to an embodiment of the invention. RLB 700 comprisesfirst and second programmable logic interfaces (PLI) 701 and 702respectively, and first and second logic clusters (LC) 707 and 711respectively. Each PLI 701 and 702 comprises a plurality of programmableswitches [CBs and SBs?] that are configurable to couple components ofRLB 700 to components of other RLBs (not shown in FIG. 7). First andsecond PLI 701 and 702 further comprise input and output buffersconfigured to communicate with CBs corresponding to RLB's on theinterconnecting grid (not shown). In one embodiment of the invention theinput buffers are provided by initializing tokens on reset. According tovarious embodiments of the invention the output buffers are configurableto perform copying operations. This enables a single output token to becopied to multiple CBs.

First and second PLIs 701 and 702 of RLB 700 comprise circuitsconfigured by implement split operations indicated at 751,752 and 753and merge operations indicated at 761,762 and 763. These operations areusable to implement 5-, 6- or 7-input functions for logic clusters 707and 711. FIG. 7 shows an RLB 700 configured as a 6-input function. Inone embodiment of the invention the splits and merges are connected tothe LUTs 721, 722, 723 and 724. In that manner RLB 700 is configured toperform logic operations on the first through sixth inputs of LUTs andto provide the result of the logic operations at RLB output 780.

Each RLB 700 includes a plurality of sources and sinks. The sourcescreate data tokens that go to and from PLI 701 and 702. These can beused as inputs for the LCs (as LUT inputs or as carry-in values).

FIG. 8 Low Latency Loops

FIG. 8 illustrates a circuit 800 comprising logic clusters 831-834. LUTs821-828 are arranged to implement a loop in accordance with anembodiment of the invention.

FIGS. 9A, 9B and 9C

FIG. 9B is a conceptual diagram illustrating an element of the fabric ofthe invention configured as a conditional unit (CU) according to anembodiment of the invention. Each RLB 700 (illustrated in FIG. 7) isconfigurable as a conditional unit (CU) as illustrated in FIG. 9A at936. In one embodiment of the invention RLB 700 comprises two 2-wayconditional units CU2, one 4-way and one 8-way conditional unit (CU2,CU4, and CU8). CU 936 is illustrated in two configurations asillustrated in FIGS. 9A and 9C. The configuration of CU 936 isdetermined by control signal 950. In a merge operation CU 936 mergesinputs i0 and i1 to provide a merged output o0. In a split operation CU936 splits an input i0 into two outputs o0 and o1.

FIG. 9C illustrates CU 936 configured to perform a split operation. CU936 reads a data token from its first input 923 and a control token fromits control channel 950. Based on the value of the control token 950, CU936 sends the data token on one of its outputs 927, 928.

FIG. 9A illustrates CU 936 configured to perform a merge operation. WhenCU 936 is configure to perform a merge operation, CU 936 reads a controltoken from 950 and, based on the value of that token, reads a data tokenfrom one of its inputs 923,924 and sends that token on its first output927.

A third configuration for a condition unit is as a deterministic MUX,which corresponds to a merge block that always receives tokens on allits inputs but only selects one of them for output. An alternative wayto configure large input functions using an RLB is to not use a splitand merge tree as shown in FIG. 7, but to copy the inputs (rather thanusing a split) and then use a deterministic MUX instead of a merge.

While the invention has been shown and described with respect toparticular embodiments, it is not thus limited. Numerous modifications,changes and enhancements will now be apparent to the reader.

What is claimed is:
 1. An apparatus, comprising: an asynchronous staticmemory block configured to operate as a first-in, first-out (FIFO)storage device; an asynchronous input reconfigurable logic block coupledto at least one input of the asynchronous static memory block, and anasynchronous output reconfigurable logic block coupled to at least oneoutput of the asynchronous static memory block; and a pair ofsynchronous input/output (I/O) blocks, a first one of the pair having anasynchronous output coupled to an input of the asynchronous inputreconfigurable logic block, and a second one of the pair having anasynchronous input coupled to an output of the asynchronous outputreconfigurable logic block.
 2. The apparatus of claim 1, wherein theasynchronous static memory block, the asynchronous input reconfigurablelogic block, and the asynchronous output reconfigurable logic block formpart of a reconfigurable logic fabric.
 3. The apparatus of claim 2,wherein the pair of synchronous I/O blocks form part of a plurality ofsynchronous I/O blocks arranged around a perimeter of the reconfigurablelogic fabric.
 4. The apparatus of claim 2, wherein the logic fabricforms a part of an integrated circuit.
 5. The apparatus of claim 1,wherein the at least one input of the asynchronous static memory blockand the at least one output of the asynchronous static memory blockcomprise a portion of a programmable number of static memory block inputports and static memory block output ports, respectively.
 6. Theapparatus of claim 1, wherein the asynchronous static memory block isconfigured to operate, at least in part, as a circular buffer with logicto support insert and remove operations.
 7. The apparatus of claim 1,further comprising: an asynchronous multiplier coupled to the staticmemory block.
 8. The apparatus of claim 7, wherein the asynchronousmultiplier comprises a programmable multiplier unit.
 9. The apparatus ofclaim 1, wherein at least one of the pair of synchronous I/O blockscomprises a configurable synchronous I/O block.
 10. The apparatus ofclaim 1, wherein at least one of the pair of synchronous I/O blockscomprises a bundled-data interface to implement an asynchronoushandshake protocol.
 11. The apparatus of claim 1, wherein at least oneof the pair of synchronous I/O blocks comprises a serial link toimplement asynchronous communication.
 12. The apparatus of claim 1,wherein each of the pair of synchronous I/O blocks comprises: aconverter unit to enable at least one of synchronous to asynchronoussignal conversion, or asynchronous to synchronous signal conversion. 13.The apparatus of claim 1, wherein at least one of the asynchronous inputreconfigurable logic block or the asynchronous output reconfigurablelogic block comprise circuit elements to enable at least one of wideAND, wide OR, or sum-of-products (SOP) operations.
 14. The apparatus ofclaim 1, wherein at least one of the asynchronous input reconfigurablelogic block or the asynchronous output reconfigurable logic blockcomprise programmable logic interfaces.
 15. The apparatus of claim 14,wherein at least one of the programmable logic interfaces comprisesswitches to couple the at least one of the asynchronous inputreconfigurable logic block or the asynchronous output reconfigurablelogic block to another asynchronous reconfigurable logic block.
 16. Theapparatus of claim 14, wherein at least one of the programmable logicinterfaces comprises input or output buffers configured to communicatewith asynchronous, programmable interconnect elements.
 17. The apparatusof claim 1, wherein at least one of the asynchronous inputreconfigurable logic block or the asynchronous output reconfigurablelogic block is configured as a conditional unit.
 18. A method,comprising: synchronously communicating information with at least one ofa pair of synchronous input/output (I/O) blocks, a first one of the paircoupled to an input of an asynchronous input reconfigurable logic block,and a second one of the pair coupled to an output of an outputasynchronous reconfigurable logic block; and asynchronously accessing afirst-in, first-out (FIFO) memory to store the information in anasynchronous static memory block, wherein the asynchronous inputreconfigurable logic block is coupled to at least one input of theasynchronous static memory block, and wherein the asynchronous outputreconfigurable logic block is coupled to at least one output of theasynchronous static memory block.
 19. The method of claim 18, furthercomprising: operating at least a portion of the asynchronous staticmemory block as a circular buffer.
 20. The method of claim 18, furthercomprising: operating the asynchronous static memory block, at least oneof the asynchronous input reconfigurable logic block or the asynchronousoutput reconfigurable logic block, and an asynchronous multiplier toimplement at least one of a fast Fourier transform (FFT), a finiteimpulse response (FIR) filter, or a discrete cosine transform (DCT).